ARIZONA’S OLDEST EXTENSIVE PERMIAN TRACKSITE AND ITS STRATIGRAPHIC SIGNIFICANCE

Along the Mogollon Rim, in the Tonto Creek area south of Payson, Arizona, siliciclastic reds beds of the lower part of the Supai Formation yield tetrapod footprints and other trace fossils from strata 19-21 meters above the stratigraphically highest marine limestone of the underlying “Naco Formation.” The trace fossils are from a stratigraphic interval 2-3 m thick of laminated sandstone beds, many of which have mudstone drapes and some of which have extensive mudcracks. A low diversity walchian-conifer-dominated paleoflora with minor, diminutive Supaia, is associated with the trace fossils. The invertebrate trace fossils are mostly assignable to Planolites, Sphaerapus, Diplichnites and Taenidium. The tetrapod footprints are mostly those of non-diapsid eureptiles (the “captorhinomorph” ichnogenera Erpetopus and Varanopus), small parareptiles or diapsids (Dromopus) and seymouriamorphs (Amphisauropus). These are footprints of the Erpetopus biochron, globally no older than Kungurian and no older than early Leonardian in New Mexico and Texas. The subsurface compaction burrow Sphaerapus is also not known from strata older than Leonardian. This means that the tracksite is no older than early Leonardian, so that all or almost all of the Supai Formation strata along the Mogollon Rim are of Leonardian age; thus, the Wolfcampian stratigraphic interval is very thin in this area. Furthermore, assigning an early Leonardian age to strata near the base of the Supai Formation on the Mogollon Rim indicates that some previous correlations of Pennsylvanian strata (e.g., Wescogame Formation) of the Supai Group in the Grand Canyon to the lower Supai Formation along the Mogollon Rim are questionable. This new tracksite is the oldest extensive Permian tracksite in Arizona and also forces a re-evaluation of age assignments to the siliciclastic red beds of the Supai Formation along the Mogollon Rim.